Method for the incorporation of a component into a piston

ABSTRACT

A porous body is formed and joined to the component by sintering a metal powder to the component. The porous body and component are placed into a piston casting die. Molten metal is poured into the die such that the porous body becomes infiltrated with the molten metal and the molten metal is allowed to solidify. The porous body may be formed by sintering loose metal powder to the component, or by forming a separate body by die pressing of metal powder and which body may be subsequently sintered and joined to the component.

This is a division of application Ser. No. 565,368 filed Aug. 10, 1990and now U.S. Pat. No. 5,094,149.

The present invention relates to the manufacture of light alloy pistonshaving components for improving one or more properties such as wearresistance, fatigue strength and thermal erosion resistance.

Aluminium alloy pistons having ferrous piston ring carrier inserts inwhich the piston ring grooves are formed in order to give improved wearresistance over the aluminium alloy are well know. They are usuallybonded to the piston body by use of the known "Alfin" process (trademark). This process produces a bond between the ferrous alloy and thealuminium alloy which is both brittle and relatively weak.

In modern highly rated diesel engines, for example, its performance ismarginal with an increasing number of field failures in engines. U.S.Pat. No. 4,334,507 describes the use of porous, sintered insertsincorporated into the piston by a pressure casting technique. It hasbeen found, however, by the present applicant that such sintered insertstend to either increase the rate of piston ring wear or that the pistonring groove wears rapidly, both of which are undesirable.

More recently, in commonly assigned British patent application number8915427.2 there is described a method whereby the ring groove insert issprayed with a coating of stainless steel powder, for example, and issubsequently encast into a piston by squeeze casting. The result of thismethod has been to virtually double the bond strength over the known"Alfin" process and to ameliorate the brittle nature of the bond betweenthe insert and the aluminium alloy.

It is an object of the present invention to improve the bond reliabilitybetween a component and the surrounding aluminium alloy still further.

According to a first aspect of the present invention a method for theincorporation of a component into a piston comprises the steps offorming and joining a porous body to the component by sintering a metalpowder to the component, placing the porous body and component into apiston casting die, pouring molten metal into the die such that theporous body becomes infiltrated with molten metal and allowing themolten metal to solidify.

It is intended that the components in question may encompass such thingsas piston ring groove reinforcement inserts, piston crown, combustionbowl inserts and bushes used for reinforcement of the gudgeon pinbosses, for example; this list being exemplary and not exhaustive.

The porous body may, in one embodiment of the method, be formed bysintering loose powder, to the component.

Alternatively, the method may comprise forming a separate porous bodyand joining the porous body to the component. The separate porous bodymay be formed, for example, by die pressing of metal powder and whichbody may be subsequently sintered and joined to the component.

The porous body may be formed from any suitable powder such as ferrousbased material or copper based material, for example. In the case ofpiston ring groove reinforcement the invention is especially beneficialwhere single sided inserts are used to improve wear resistance of thelower ring groove face only.

The present invention may also be combined with spraying of certainfaces of the components such as is described in GB 8915427.2 of commonownership herewith.

According to a second aspect of the present invention there is provideda piston having at least one component incorporated therein when made bythe method of the first aspect.

In order that the present invention may be more fully understood,examples will now be described by way of illustration only withreference to the accompanying drawings, of which:

FIG. 1 shows a section through a single sided piston ring groovereinforcement having a porous body attached thereto;

FIG. 2 shows a first modification of the embodiment of FIG. 1;

FIG. 3 shows a second modification of the embodiment of FIG. 1;

FIG. 4 shows a full piston ring groove reinforcement having porousbodies attached thereto;

FIG. 5 shows a modification of the embodiment of FIG. 4;

FIG. 6 shows a piston having a combustion bowl insert and gudgeon pinboss bushes; and

FIG. 7 shows a ring groove reinforcement insert having a layer of powdersintered directly to it.

Referring now to FIG. 1 and where the top ring groove region of thecrown end of a piston is denoted at 10. The comprises analuminium-silicon alloy body 12. The piston ring groove 14 has a lowerface 15 machined into an annular, austenitic cast iron insert 16 towhich is bonded by brazing, a porous ring 18. The piston crown is shownafter machining; the chain dotted lines 20 indicating the profiles ofthe components after casting of the piston body and prior to machining.The porous ring 18 is produced by die pressing of an appropriate powderfollowed by sintering and is first brazed to the lower face 22 of theinsert 16 with sufficient material to provide a strong bond but alsoensuring that sufficient porosity remains to allow impregnation of theporosity by the aluminium alloy which is cast by a known squeeze castingtechnique. The rear curved face 23 of the insert may be sprayed with astainless steel powder as described in GB 8915427.2.

FIG. 2 shows a modification where the annular porous body 18 has an`L`-shaped section which when brazed to the ring groove reinforcinginsert 16 provides a strong bond to the piston alloy on both faces 22and 24.

FIG. 3 shows an insert which effectively has only one face, 26, bondedto the piston body after machining.

FIG. 4 shows a full piston ring groove reinforcing member 30 having twoporous bodies 32, 34 brazed on. The body 32 has an `L`-shaped crosssection whilst body 34 is a flat ring.

FIG. 5 shows an insert 40 having two, flat porous rings 42, 44 brazed tothe upper and lower, generally radially extending faces 46, 48. Therear, generally axially directed face 50 has a plasma sprayed coating 52of a stainless steel powder. The squeeze cast piston alloy 54infiltrates the micro porosity of the sprayed coating 52 in addition tothe flat rings 42, 44 and provides a strong bond.

FIG. 6 shows a piston 60 having a combustion bowl insert 62 to which isbrazed a porous, generally cup-shaped body 64. Bronze bushes 66, toreinforce the gudgeon pin cross-holes 68, have porous bronze bushes 70brazed onto their outer diameters 72.

FIG. 7 depicts an austenitic iron ring 80 intended to reinforce thepiston ring groove of a piston (not shown). The ring 80 has sintered toit a layer 82 of a bronze 10% tin--powder having generally sphericalparticles of between--85 and +120 B.S. mesh. To form the layer 82 afirst layer 84 of the powder is placed in a die 86 having a central core88, the die and core being made of graphite. The iron ring 80 which hasa copper plated layer 90 is then placed on the first layer 84. Morepowder is then added to fill the annular space 92 and provide a surface94 level with the upper die surface 96. The complete assembly of die,core, ring and powder is then placed in a conveyor furnace having areducing atmosphere of 25% vol. hydrogen and 75% vol. nitrogen and issintered at approximately 835° C. for 10 minutes. After sintering thepowder strongly adheres to the ring and which may be incorporated into apiston as described above.

Although squeeze casting has been given above as the example of apressure casting technique it is intended to encompass any castingtechnique which is operated at other than ambient pressure. Thus, vacuumor reduced pressure infiltration, for example, is also deemed to beincluded as a pressure casting technique.

I claim:
 1. A method for the incorporation of a component into a piston,the method comprises the steps of forming and joining a porous body tothe component by sintering a metal powder to the component, placing theporous body and component into a piston casting die, pouring moltenmetal into the die such that said porous body becomes infiltrated withsaid molten metal and allowing said molten metal to solidify.
 2. Amethod according to claim 1 wherein the component is one or moreselected from the group consisting of piston ring groove reinforcement,piston crown, combustion bowl, gudgeon pin boss bore reinforcements. 3.A method according to claim 1 wherein said porous body is a separatebody formed from a metal powder.
 4. A method according to claim 1wherein said forming and joining of said porous body is by sintering aloose metal powder to said component.
 5. A method according to claim 1wherein said porous body is formed from either a ferrous based powder ora copper based powder.
 6. A method according to claim 1 wherein saidporous body is infiltrated by squeeze casting of the molten metal.
 7. Amethod according to claim 1 wherein said porous body is infiltrated by avacuum or reduced pressure casting technique.
 8. A method according toclaim 4 wherein said loose metal powder is located in a die.
 9. A methodaccording to claim 3 wherein said metal powder is located in a die. 10.A method according to claim 9 wherein said metal powder is die pressedin said die prior to said sintering.